The present invention relates generally to barcode scanners, and more specifically, to scanning efficiency thereof.
In a typical barcode scanner, a laser emits a beam which sweeps across a barcode and reflects a portion of the light back into the scanner. A typical one-dimensional barcode includes a series of alternating dark bars and white spaces of varying width which encode therein any desired information or data.
As the laser beam sweeps across the bars and spaces, light is absorbed by the dark bars and reflected off the white spaces at a data frequency or rate which varies as a function of the sweep speed and width of the bars and spaces. The faster the sweep and the smaller the width the higher the data rate, and the slower the sweep and larger the width the lower the data rate. And, as the distance of the barcode from the scanner increases, the data rate also increases, and the reflected light becomes weaker.
In a typical barcode scanner, a rotary spinner having a plurality of mirrored facets divides the laser beam into a corresponding number of segments which are reflected off a plurality of differently oriented pattern mirrors to form scan lines which project in an intersecting pattern once per revolution of the spinner. This maximizes the ability to scan a barcode placed at any orientation within the field of view of the scanner.
The light reflected from the barcode typically follows the reverse scanning path through the pattern mirrors and spinner to a collection mirror that focuses the light onto a photodetector to produce a corresponding electrical signal which is decoded in a suitable digital processor or decoder.
Since the reflected laser beam is relatively weak, the collection optics require suitably large size to maximize collected light within a reasonable scanner envelope for maximizing available signal to noise and improve scanning detection capability. Furthermore, since barcodes come in various sizes and may be positioned at various distances from the scanner, the scanner requires a relatively wide bandwidth video processing circuit for resolving the reflected laser beam at various data rates in a typical range of about 0.1-1.0 MHz.
However the wide bandwidth required for the varying data rate results in a correspondingly small signal gain in the video circuit. The small gain requires suitable signal strength from the photodetector, and correspondingly requires a suitably large area of the collection optics for capturing sufficient reflected light for completing a successful scan.
Accordingly, it is desired to increase scanner efficiency and reduce complexity and size thereof.